Conventional union nuts are permanently installed on pipes after the piping tailpieces are in place. In high pressure air systems, particularly on military ships, union nuts are used throughout the system (numbering in the hundreds) to secure mechanical joints. These shipboard high pressure air systems are often subject to changes in temperature and humidity. Shipboard air systems also have an operating pressure of over three thousand pounds per square inch. Union nuts need to be resilient to these changes. Historically, military vessel air systems have been outfitted with union nuts manufactured from either stainless steel or nickel aluminum bronze. However, in newer installations, silicon aluminum bronze is used. Silicon aluminum bronze, due to its metallurgical structure, has a lower corrosion resistance, making it is more susceptible to failure in high humidity, high pressure environments. Consequently, it can be substandard material for some extreme environments. On many Navy vessels, the high pressure, high temperature, high humidity environment has caused silicon aluminum bronze union nuts to corrode, crack and split. These union nuts, and others that have been identified as susceptible to failure, need to be replaced to maintain the integrity and safety of the ship's high pressure air system.
Conventionally, replacing the union nut required cutting the pipe to remove the failed union nut, repairing or replacing the pipe and tail piece, and installing a new union nut, even when the pipe and tailpiece were undamaged. This repair and replacement is costly, time consuming and labor intensive. Replacing pipe and tailpiece requires “hot work,” such as welding or brazing. Then, subsequent system cleaning, flushing, testing, and inspections are required. Consequently, what is needed is a more convenient and effective method for replacing failed or sub-standard union nuts without having to cut out and replace sections of pipe and conduct all of the associated tests and inspections of the system.